Pressure electrolyzer and method for switching off a pressure electrolyzer

ABSTRACT

A pressure electrolyser having a pressure reservoir, an electrolytic cell block containing a number of electrolytic cells and positioned in the pressure reservoir, the electrolytic cells each containing anodes and cathodes, and an electrolyte circulatory system for supplying electrolyte to the anodes and cathodes. The circulatory system includes an oxygen separator operative to separate gaseous oxygen formed during operation of the pressure electrolyser and a hydrogen separator operative to separate gaseous hydrogen formed during operation of the pressure electrolyser, and a store of an inert gas, to inert the pressure electrolyser when it is switched off. The store of inert gas is supplied to the oxygen separator. The electrolyte circulatory system further includes a connecting line arranged so that a part of the electrolyte can be pushed out of the hydrogen separator when the inert gas is applied to the oxygen separator so as to displace the gaseous hydrogen.

The invention relates to a pressure electrolyser in accordance with thepre-characterising clause of claim 1, and a process for switching off apressure electrolyser in accordance with the pre-characterising clauseof claim 9.

Pressure electrolysers which comprise a pressure reservoir and anelectrolytic cell block which is positioned in the pressure reservoirand contains a number of electrolytic cells combined in the form of astack are known for the electrolytic splitting of water into hydrogenand oxygen. The electrolytic cells contain anodes and cathodes, and anelectrolyte circulatory system is provided for supplying electrolyte tothe anodes and cathodes. An oxygen separator serves to separate thegaseous oxygen formed during the operation of the pressure electrolyserand a hydrogen separator serves to separate the gaseous hydrogen formedduring the operation of the pressure electrolyser. In order to inert thepressure electrolyser when it is switched off a store of an inert gas,in particular nitrogen, is provided.

A pressure electrolyser of traditional type is known from DE 25 48 699C3, for example.

A vital safety factor in pressure electrolysers of the type specifiedlies in their capacity to be inerted quickly, reliably and fully, i.e.in the removal of the hydrogen from the pressure reservoir and from thehydrogen separator, such that the residual hydrogen content is wellbelow the lower explosion limit of 4% by vol.

Traditionally, large quantities of inert gas, typically nitrogen, areheld ready for inerting, it being used to rinse the hydrogen out of thehydrogen separator when the electrolyser is switched off, in the eventof an emergency shutdown, for example. To this end the pressure in thepressure electrolyser may either be maintained or reduced to ambientpressure in the course of rinsing with the inert gas. In any event, dueto the mixing of the gases a, multiple of the gas volume of the hydrogenseparator must be held ready in the form of inert gas. Since, due to theevolution of hydrogen or oxygen in hidden caverns, decompressing theelectrolyser at speed typically causes damage to the seals andstructural components of the cells and means that the subsequentrestarting of the unpressurised plant is associated with considerableenergy expenditure, the electrolyser should, where possible, only bedecompressed in three, genuinely unavoidable emergency scenarios: anelectrolyte leak, a product gas leak or a critical impurity in theproduct gas. In all other cases pressure should be maintained when theelectrolyser is switched off.

The object of the invention is to create a pressure electrolyser and aprocess for switching off a pressure electrolyser in which the reliableinerting of the electrolyser is possible with a minimum amount of inertgas. In particular, but not exclusively, it should be possible to switchoff the electrolyser without decompressing it.

This object is achieved in relation to the device by means of a pressureelectrolyser with the features of claim 1.

This object is achieved in relation to the process by means of a processwith the features of claim 9.

Advantageous versions of the invention are specified in the varioussubsidiary claims.

The invention creates a pressure electrolyser with a pressure reservoirand an electrolytic cell block which is positioned in the pressurereservoir and contains a number of electrolytic cells. The electrolyticcells contain anodes and cathodes and an electrolyte circulatory systemis provided for supplying electrolyte to the anodes and cathodes. Anoxygen separator is provided to separate the gaseous oxygen formedduring the operation of the pressure electrolyser and a hydrogenseparator is provided to separate the gaseous hydrogen formed during theoperation of the pressure electrolyser. A store of an inert gas, inparticular nitrogen, serves to inert the pressure electrolyser when itis switched off. In the invention the store of inert gas can be suppliedto the oxygen separator and the electrolyte circulatory system containsa connecting line via which a part of the electrolyte can be pushed outof the hydrogen separator when the inert gas is applied to the oxygenseparator, thereby displacing the gaseous hydrogen.

In one version of the pressure electrolyser disclosed in the invention,the oxygen separator and/or the hydrogen separator is provided outsidethe pressure reservoir and when the inert gas is applied to the oxygenseparator a part of the electrolyte can be pushed from the pressurereservoir and/or the oxygen separator into the hydrogen separator inorder to displace the hydrogen in the hydrogen separator.

In another preferred version of the invention the oxygen separatorand/or the hydrogen separator is formed by a part of the volume withinthe pressure reservoir and when the inert gas is applied to the oxygenseparator a part of the electrolyte can be pushed into the part of thepressure reservoir which forms the hydrogen separator in order todisplace the hydrogen, in particular within the pressure reservoir.

In one version of the invention the connecting line via which a part ofthe electrolyte can be pushed out of the hydrogen separator bydisplacing the hydrogen is provided outside the pressure reservoir.

In this arrangement, the connecting line may take the form of a shuttleline which runs beneath the liquid level of the electrolyte and connectsthe oxygen separator to the hydrogen separator.

In an alternative version of the pressure electrolyser disclosed in theinvention the connecting line via which a part of the electrolyte can bepushed out of the hydrogen separator, thereby displacing the hydrogen,is provided inside the pressure reservoir.

In an advantageous version of the pressure electrolyser disclosed in theinvention, the housing of the electrolytic cell block and the pressurereservoir together form at least two separate chambers which are part ofthe electrolyte circulatory system and which are delimited from theelectrolytic cells by the housing and from the environment by thepressure reservoir, one of the separate chambers being part of ananolyte circuit and connected to the oxygen separator and another of theseparate chambers being part of a catholyte circuit and connected to thehydrogen separator.

In this arrangement, the separate chambers can be separated by dividingwalls which extend from the housing of the electrolytic cell block andthe pressure reservoir and the connecting line, via which a part of theelectrolyte can be pushed out of the hydrogen separator, therebydisplacing the hydrogen, can be formed by a passage in an area of thedividing walls which lies below the liquid level of the electrolyte.

Furthermore, the invention also creates a process for switching off apressure electrolyser, the pressure electrolyser containing a pressurereservoir and an electrolytic cell block which comprises a number ofelectrolytic cells and is positioned in the pressure reservoir, theelectrolytic cells containing anodes and cathodes and an electrolytecirculatory system being provided for the supply of electrolyte to theanodes and cathodes. An oxygen separator serves to separate the gaseousoxygen formed during the operation of the pressure electrolyser and ahydrogen separator serves to separate the gaseous hydrogen formed duringthe operation of the pressure electrolyser. To inert the pressureelectrolyser, an inert gas, in particular nitrogen, is fed into thepressure electrolyser when it is switched off. In the invention, theinert gas is fed into the oxygen separator and when the inert gas isapplied to the oxygen separator a part of the electrolyte is pushed outof the hydrogen separator via a connecting line provided in theelectrolyte circulator system, thereby displacing the gaseous hydrogen.

In an advantageous version of the process disclosed in the invention theoxygen separator and/or the hydrogen separator is provided outside thepressure reservoir and when the inert gas is applied to the oxygenseparator a part of the electrolyte is pushed from the pressurereservoir and/or from the oxygen separator into the hydrogen separatorin order to displace the hydrogen in the hydrogen separator.

In another advantageous version of the process disclosed in theinvention the oxygen separator and/or the hydrogen separator is formedby a part of the volume inside the pressure reservoir and when the inertgas is applied to the oxygen separator a part of the electrolyte ispushed into the part of the pressure reservoir volume forming thehydrogen separator in order to displace the hydrogen, in particularinside the pressure reservoir.

Various embodiments of the invention are explained below with referenceto the drawings.

FIGS. 1 a) and 1 b) show a schematised view of a pressure electrolyseras disclosed in the invention in operating mode (FIG. 1 a) and inswitched-off mode (FIG. 1 b).

FIGS. 2 a) and 2 b) show a schematised view of a pressure electrolyseras disclosed in the invention in operating mode (FIG. 2 a) and inswitched-off mode (FIG. 2 b).

In FIGS. 1 a), 1 b), 2 a) and 2 b) a pressure electrolyser referred toin its totality by the reference numerals (11/31) and used for theelectrolytic splitting of water into hydrogen and oxygen comprises apressure reservoir (12/32) in which is positioned an electrolytic cellblock (13/33). The electrolytic cell block (13/33) consists of a numberof electrolytic cells (14/34) combined in the form of a stack which areindicated only generally in the drawings. The electrolytic cells (14)each contain an anode and a cathode (not illustrated). An electrolytecirculatory system (of which only part is illustrated in the drawings)serves to supply electrolyte to the anodes and cathodes. An electrolyserof this type is described in the unpublished German patent applicationwith the reference no. 101 50 557.4, for example.

In addition to the pressure reservoir (12), the embodiment illustratedin FIGS. 1 a) and 1 b) also contains an oxygen separator (21) forseparating the gaseous oxygen formed when the pressure electrolyser (11)is in operation and a hydrogen separator (22) for separating the gaseoushydrogen formed when the pressure electrolyser (11) is in operation.

In the embodiment illustrated in FIGS. 2 a) and 2 b), the housing (35)of the electrolytic cell block (33) together with the pressure reservoir(32) forms two separate chambers (37, 38) which are separated from oneanother by dividing walls (39, 40) which extend between the housing (35)of the electrolytic cell block (33) and the pressure reservoir (32). Thetwo separate chambers (37, 38) form part of the electrolyte circulatorysystem and are delimited from the electrolytic cells (34) by the housing(35) and from the environment by the pressure reservoir (32).

A part of the volume inside the pressure reservoir (32) which is locatedabove the electrolytic cell block (33) forms an oxygen separator (41)for separating the gaseous oxygen formed during the operation of thepressure electrolyser (31) and a part of the volume inside the pressurereservoir (32) which is also located above the electrolytic cell block(33) forms a hydrogen separator (42) for separating the gaseous hydrogenformed during the operation of the pressure electrolyser (31).

Of the two aforementioned separate chambers (37, 38) which form part ofthe electrolyte circulatory system, one, namely chamber (37), is part ofan anolyte circuit and is connected to the part of the volume inside thepressure reservoir (32) which forms the oxygen separator (41), while theother chamber (38) is part of a catholyte circuit and is connected tothe part of the volume inside the pressure reservoir (32) which formsthe hydrogen separator (42).

In all the embodiments illustrated a store of an inert gas, inparticular nitrogen, is provided for inerting the pressure electrolyser(11/31) when it is switched off. This store is not, however, illustratedin the drawings. This inert gas serves to rid the pressure electrolyser,and in particular the hydrogen separator (22/42), of hydrogen at leastto the extent that the hydrogen content lies below the lower explosionlimit of 4% by vol. In general terms, this store of inert gas or theinert gas held ready can be fed into the oxygen separator (21/41) insuch a manner that when the inert gas is applied to the oxygen separator(21/41) a part of the electrolyte within the electrolyte circuit ispushed in such a manner that the gaseous hydrogen is forced out of thehydrogen separator (22/42). In this arrangement, the displaced hydrogenmay be discharged into the environment, stored or removed in anothermanner, for example.

In order that the electrolyte in the electrolyte circulatory system canbe pushed out of the hydrogen separator (22/42) as described above,thereby displacing the gaseous hydrogen, a connecting line (23 a; 23 b;42 a; 43 b) is provided in the electrolyte circulatory system which maybe of various designs.

In the embodiment illustrated in FIGS. 1 a) and 1 b) the aforementionedconnecting line is provided outside the pressure reservoir (12), twodifferent versions thereof being illustrated in the same diagram. Forexample, the connecting line running outside the pressure reservoir (12)may be formed either by a connecting line (23 a) which connects a volumearea associated with the oxygen separator (21) inside the pressurereservoir (12) to a volume area associated with the hydrogen separator(22) inside the pressure reservoir (12), or by a shuttle line (23 b)which connects the oxygen separator (21) to the hydrogen separator (22)and runs beneath the liquid level of the electrolyte. Finally, theaforementioned connecting line may also connect an area of theelectrolyte circuit associated with the oxygen separator (21) to an areaof the electrolyte circuit associated with the hydrogen separator (22)inside the pressure reservoir (12) (although this version is notillustrated in FIGS. 1 a) and 1 b)).

In the normal operating mode of the pressure electrolyser (11)illustrated in FIG. 1 a), any oxygen formed is collected in the oxygenseparator (21) and any hydrogen formed is collected in the hydrogenseparator (22). Parts (namely the bottom) of both the oxygen separator(21) and the hydrogen separator (22) are filled with electrolyte, whilethe product gas in question collects in the upper area of the separator(21, 22).

When the pressure electrolyser (11) needs to be switched off, the inertgas held ready, typically nitrogen, is fed into the oxygen separator(21), typically in the upper volume area provided for the collection ofthe gaseous oxygen. Part of the electrolyte is then pushed via theconnecting line (23 a, 23 b) provided in the electrolyte circuit out ofthe oxygen separator (21) and/or out of the pressure reservoir (12) intothe hydrogen separator (22) where it displaces the gaseous hydrogen insaid hydrogen separator (22), thereby inerting the pressure electrolyser(11) and the hydrogen separator (22). This inerting process does notusefully take place until essentially all the gaseous hydrogen has risenout of the pressure reservoir (12) into the hydrogen separator (22).FIG. 1 b) shows the pressure electrolyser (11) in its switched-off,inerted state.

In the embodiment illustrated in FIGS. 2 a) and 2 b) the connecting line(43 a, 43 b) via which a part of the electrolyte can be pushed out ofthe volume area of the pressure reservoir (32) forming the hydrogenseparator (42), thereby displacing the gaseous hydrogen, is eitherformed by a connecting line (43 a) running outside the pressurereservoir (32) which connects a chamber (37) forming the volume area ofthe pressure reservoir (32) associated with the oxygen separator (41),i.e. one part of the anolyte circuit, to a chamber (38) forming thevolume area of the pressure reservoir (32) associated with the hydrogenseparator (42), i.e. one part of the catholyte circuit, or there isprovided inside the pressure reservoir (32) a connecting line (43 b)which connects a chamber (37) forming the volume area of the pressurereservoir (32) associated with the oxygen separator (41), i.e. one partof the anolyte circuit, to a chamber (38) forming the volume area of thepressure reservoir (32) associated with the hydrogen separator (42),i.e. one part of the catholyte circuit. This connecting line (43 b) istypically provided in the dividing wall (40) beneath the electrolyticcell block (33).

When inerting the electrolyser (31), the inert gas held ready, typicallynitrogen, is applied to volume area of the pressure reservoir (32)forming the oxygen separator (41), thereby transferring the electrolytevia the connecting line (43 a/43 b) out of the volume area of thepressure reservoir (32) associated with the oxygen separator (41), i.e.out of the chamber (37) of the anolyte circuit, into the volume area ofthe pressure reservoir (32) associated with the hydrogen separator (42),i.e. into the chamber (38) of the catholyte circuit, until the hydrogenhas been completely removed from the volume area of the pressurereservoir (32) forming the hydrogen separator (42). Here, once again,inerting does not usefully take place until essentially all the hydrogenformed has collected in the hydrogen separator (42), i.e. in thecorresponding volume area of the pressure reservoir (32).

In all the embodiments detailed, the pushing of the electrolyte levelinto the hydrogen separator (22/42) can be monitored by appropriatemeans, for example by level detectors which monitor the rise in level ofthe electrolyte in the hydrogen separator (22/42) up to a predeterminedlevel.

The hydrogen displaced during the inerting of the hydrogen separator(22/42) can be stored and used again. It must not be disposed of sinceit is not mixed with the inert gas fed in.

The invention may be used with all types of electrolysers including, forexample, PEM electrolysers which use water as the electrolyte.

1-11. (canceled)
 12. A pressure electrolyser, comprising: a pressurereservoir; an electrolytic cell block containing a number ofelectrolytic cells and positioned in the pressure reservoir, theelectrolytic cells each containing anodes and cathodes; and anelectrolyte circulatory system for supplying electrolyte to the anodesand cathodes, the circulatory system including an oxygen separatoroperative to separate gaseous oxygen formed during operation of thepressure electrolyser and a hydrogen separator operative to separategaseous hydrogen formed during operation of the pressure electrolyser,and a store of an inert gas to inert the pressure electrolyser when itis switched off, the store of inert gas being supplyable to the oxygenseparator, the electrolyte circulatory system further including aconnecting line arranged so that a part of the electrolyte can be pushedout of the hydrogen separator when the inert gas is applied to theoxygen separator so as to displace the gaseous hydrogen.
 13. A pressureelectrolyser in accordance with claim 12, wherein the oxygen separatorand/or the hydrogen separator is arranged outside the pressure reservoirso that when the inert gas is applied to the oxygen separator a part ofthe electrolyte is pushed by the pressure reservoir and/or by the oxygenseparator into the hydrogen separator in order to displace the hydrogenin the hydrogen separator.
 14. A pressure electrolyser in accordancewith claim 12, wherein the oxygen separator and/or the hydrogenseparator is formed by a part of the volume inside the pressurereservoir so that when the inert gas is applied to the oxygen separator,a part of the electrolyte is pushed into the part of the pressurereservoir volume forming the hydrogen separator in order to displace thehydrogen.
 15. A pressure electrolyser in accordance with claim 12,wherein the connecting line is arranged outside the pressure reservoir.16. A pressure electrolyser in accordance with claim 13, wherein theconnecting line is arranged outside the pressure reservoir, theconnecting line being formed by a shuttle line that runs beneath theliquid level of the electrolyte and connects the oxygen separator to thehydrogen separator.
 17. A pressure electrolyser in accordance with claim12, wherein the connecting line is provided inside the pressurereservoir.
 18. A pressure electrolyser in accordance with claim 12,wherein the electrolytic cell block has a housing that together with thepressure reservoir forms at least two separate chambers which are partof the electrolyte circulatory system and which are delimited from theelectrolytic cells by the housing and from the environment by thepressure reservoir, one of the separate chambers being part of ananolyte circuit and connected to the oxygen separator and another of theseparate chambers being part of a catholyte circuit and connected to thehydrogen separator.
 19. A pressure electrolyser in accordance with claim18, wherein the separate chambers are separated from one another bydividing walls which extend between the housing of the electrolytic cellblock and the pressure reservoir, the connecting line being formed by apassage in an area of the dividing walls beneath the liquid level of theelectrolyte.
 20. A process for switching off a pressure electrolyserwhich comprises a pressure reservoir and an electrolytic cell blockcontaining a number of electrolytic cells and positioned in the pressurereservoir, the electrolytic cells each containing anodes and cathodesand an electrolyte circulatory system for supplying electrolyte to theanodes and cathodes, an oxygen separator to separate gaseous oxygenformed during operation of the pressure electrolyser and a hydrogenseparator to separate gaseous hydrogen formed during operation of thepressure electrolyser being provided, an inert gas, the processcomprising the steps of: switching off the pressure electrolyser; andfeeding inert gas to the oxygen separator so that a part of theelectrolyte is pushed out of the hydrogen separator via a connectingline contained in the electrolyte circulatory system, thereby displacingthe gaseous hydrogen.
 21. A process in accordance with claim 20, whereinthe oxygen separator and/or the hydrogen separator is provided outsidethe pressure reservoir, and when the inert gas is applied to the oxygenseparator, pushing a part of the electrolyte is pushed by the pressurereservoir and/or the oxygen separator into the hydrogen separator inorder to displace the hydrogen in the hydrogen separator.
 22. A processin accordance with claim 20, wherein the oxygen separator and/or thehydrogen separator is formed by a part of the volume inside the pressurereservoir, and when the inert gas is applied to the oxygen separator,pushing a part of the electrolyte is pushed into the pressure reservoirvolume forming the hydrogen separator in order to displace the hydrogen.23. A process in accordance with claim 20, wherein the inert gas isnitrogen.